Astronauts fix cooling pump in third spacewalk

August 16, 2010|By Mark K. Matthews, Orlando Sentinel

WASHINGTON -- The International Space Station should be back to normal in a couple days after NASA astronauts Doug Wheelock and Tracy Caldwell Dyson cruised through a seven-hour spacewalk Monday to successfully install a cooling pump to replace one that broke July 31.

Early readings show that everything on the new pump was working fine; NASA hopes to have it fully operational no later than Thursday. Wheelock celebrated the end of all major work during the mission when he breathed a relieved "game over" to ground control.

The spacewalk was the third devoted to replacing the pump. On the first two, Wheelock and Caldwell Dyson spent most of their time removing the broken one, as they could not completely detach the 780-pound pump on the first go-around because of problems disconnecting a cooling line.

The first spacewalk on Aug. 7, at longer than eight hours, set a record as the longest ever at the station. Monday's mission was clocked at 7 hours and 20 minutes. It was the sixth spacewalk for Wheelock and the third for Caldwell Dyson.

Since the old pump first failed in a nighttime incident that set off alarm bells, the station has relied on one American pump -- instead of the usual two -- to keep it from overheating. With just one pump going, the crew has powered down some non-essential equipment to avoid overtaxing it.

The six-member crew has never been in danger in the past two weeks, and using one pump has barely affected station operations. But NASA has moved quickly to replace the broken pump because the crew would have to take draconian steps to shut down equipment in case both pumps died.

In that event, the crew would have to rely on the Russian section -- which is powered and cooled by a different system -- to handle the workload until NASA could bring at least one pump back online. But that scenario appears remote after Monday's successful spacewalk.

Three spare pumps remain to help the $100-billion station reach its goal of operating until at least 2020. Keeping enough backup equipment onboard has been an ongoing concern, especially with NASA's decision to retire the space shuttle, and its massive payload bay, next year.

Recent shuttle flights largely have been devoted to bringing spare equipment and science experiments up to the station, and the remaining two missions will have the same purpose. Congress has pushed the White House to add a third shuttle flight sometime in 2011 to bring up one last round of supplies.

Once the shuttle is grounded, NASA must rely on Russia and other international partners to ferry crew and cargo to the station until a US replacement is ready. The options being debated include increased use of commercial vehicles and the construction of a new in-house NASA spacecraft.The spare pump being installed today was delivered to the station aboard space shuttle Discovery in July 2006.